During a typical semiconductor wafer fabrication process it is necessary to subject the wafer to a plurality of cleaning steps. Etching compounds, polishes, solvents, abrasives, and other chemicals used for deposition or polishing methods often leave residues on the wafer. Such contaminants can increase defectivity or deteriorate electrical performance of the wafer components, and are consequently rinsed or otherwise removed to clean the wafer. An effective wafer cleaning includes both of a thorough rinsing process and a quick drying process. Many benefits gained by an effective rinsing step can be lost if the drying step is not carefully carried out.
One common method for cleaning a semiconductor wafer is spin rinse drying, which involves mounting a wafer on a chuck and spraying the wafer with a cleaning solvent while the wafer is spinning. A desirable feature of spin rinse drying is the ability to dry each wafer individually and not in batches. Integrated circuits are commonly manufactured individually, with processing steps including implantation, deposition, etching, etc. performed on one substrate at a time. Spin rinse drying allows for the cleaning processes to be performed in line with the other processing steps, removing the need to wait for a certain number of wafers to be ready for combined cleaning.
Some spin rinse drying processes utilize the wind created during spinning to dry the cleaning liquid. Air drying the wafer surface in this manner is somewhat counterproductive because particulates that were dissolved in the liquid tend to remain on the wafer surface after the liquid evaporates. Also, streak marks are often left on the wafer surface when drying is performed in this manner. The wafer outer regions spin with a greater velocity than the wafer inner regions, and the wafer outer regions are consequently the first areas to dry. When a rotational force causes liquid to spread from the wafer inner areas over the dry outer surface, particulates in the liquid will sometimes create the streak mark.
One improved spin rinse drying apparatus is illustrated in FIGS. 1A and 1B. A wafer 10 rotates at a speed ω while a liquid 16 is delivered to the wafer surface through a dispense tube 12 that slowly moves from the substrate center towards the edge at a speed ν. A second nozzle 14 is mounted on the trailing side of the liquid dispense tube 12. The second nozzle 14 dispenses a tensioactive vapor that reduces the liquid surface tension and creates a strong force, commonly referred to as the Marangoni force, tangential to the wafer surface. The interaction of the rotational force with the Marangoni force physically removes the liquid from the wafer surface instead of allowing the liquid to evaporate.
Although the method described above, combining the Marangoni force with rotational force, provides a cleaner wafer than a conventional spin drying process, there are still some inherent limitations that impede the production of a wafer that is substantially free of streak marks or other particulate residue. One such limitation is that the back-side of the wafer must still be dried by a conventional spin dry process after the front-side is dried with a combination of Marangoni and rotational forces. The high speeds used in back-side dry process may cause splash back of liquid droplets that may accumulate on the cell walls, and worse, onto the wafer front side. Splash back may be prevented by using a low speed process, but drying is inherently slow at low speeds.
Another limitation typically associated with spin drying is the relatively slow drying speed. Both the front and back sides of a wafer should be free of contaminants prior to use. Spin drying is typically performed with one side of the wafer being exposed to one or more rinse and dry nozzles, with the opposite side being supported by a spinning chuck and therefore inaccessible to the rinse and dry nozzles.
Accordingly, it is desirable to provide a rinsing and drying apparatus and method that enable removal of rinsing liquid and the particulates dissolved therein on both the front and back sides of a wafer simultaneously. In addition, it is desirable to provide a rinsing and drying apparatus and method that produces a wafer or other workpiece substantially free of particulates due to liquid streaking or evaporation residue. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.